Hi, Maureen
The only thing aerobic I can think of which doesn't use or swing your arms is the stationary bike. Do you have one at home, or access to a gym or YWCA? (I also thought of paddle-boating, but doubt if many of us have access to a paddle boat!)
As a general observation, my understanding is if you exercise any body part, the rest of your body will maintain fitness to a certain degree. In other words, if you break your right leg & continue to hop around & exercise your left leg, your right leg will be in far better shape when the cast comes off than if you did no exercise at all. I remember reading this in a study. I guess every little thing helps!
Also, if it makes you feel any better, I took a hiatus from any working out (except walking the dog) for about 6 months, and when I finally got myself to start over again, I was in far better shape than when I originally started working out for the first time. I also built up strength & stamina much faster. It was a very pleasant surprise! Good luck with it, I'm sure you'll be feeling better soon & will find your fitness to be in decent shape.